Biotic and abiotic constraints that facilitate host exclusivity of Gondwanamyces and Ophiostoma on Protea

Abstract:

Estimations of global fungal diversity are hampered by a limited understanding of the
forces that dictate host exclusivity in saprobic microfungi. To consider this problem for
Gondwanamyces and Ophiostoma found in the flower heads of Protea in South Africa, we
determined the role of various factors thought to influence their host exclusivity. Results
showed that various biotic and abiotic factors influence the growth and survival of these
fungi in vitro. Monitoring temperature and relative humidity (RH) fluctuations within
infructescences in vivo revealed considerable microclimatic differences between different
Protea spp. Fungal growth and survival at different RH levels experienced in the field
suggested that this factor does not play a major role in host exclusivity of these fungi. Maximum
temperatures within infructescences and host preferences of the vectors of Gondwanamyces
and Ophiostoma appear to play a substantial part in determining colonisation of
Protea in general. However, these factors did not explain host exclusivity of specific fungal
species towards particular Protea hosts. In contrast, differential growth of fungal species on
media containing macerated tissue of Protea showed that Gondwanamyces and Ophiostoma
grow best on tissue from their natural hosts. Thus, host chemistry plays a role in host
exclusivity of these fungi, although some species grew vigorously on tissue of Protea spp.
with which they are not naturally associated. A combination of host chemistry and
temperature partially explains host exclusivity, but the relationship for these factors on
the tested saprobic microfungi and their hosts is clearly complex and most likely includes
combinations of various biotic and abiotic factors including those emerging from this
study.